Lead the Bit Rotary Steerable Tool

ABSTRACT

In one aspect of the present invention, a drilling assembly comprises a drill bit comprising a bit body intermediate a working face and a shank. An indenting member adapted to guide the drill bit protrudes from the working face. A flexible portion is disposed above the bit body.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 12/362,661 which is a continuation-in-part of U.S.patent application Ser. No. 11/837,321, which is a continuation-in-partof U.S. patent application Ser. No. 11/750,700, which is acontinuation-in-part of U.S. patent application Ser. No. 11/737,034,which is a continuation-in-part of U.S. patent application Ser. No.11/686,638 which is a continuation-in-part of U.S. patent applicationSer. No. 11/680,997 which is a continuation-in-part of U.S. patentapplication Ser. No. 11/673,872 which is a continuation-in-part of U.S.patent application Ser. No. 11/611,310, which is a continuation-in-partof U.S. patent application Ser. No. 11/278,935 which is acontinuation-in-part of U.S. patent application Ser. No. 11/277,294which is a continuation-in-part of U.S. patent application Ser. No.11/277,380 which is a continuation-in-part of U.S. patent applicationSer. No. 11/306,976 which is a continuation-in-part of U.S. patentapplication Ser. No. 11/306,307 which is a continuation-in-part of U.S.patent application Ser. No. 11/306,022 which is a continuation-in-partof U.S. patent application Ser. No. 11/164,391. All of theseapplications are herein incorporated by reference in their entirety andtheir priorities claimed.

BACKGROUND OF THE INVENTION

This invention relates to the field of tools used in directionaldrilling. More specifically, the invention includes a flexible portiondisposed in a drill string to facilitate drilling inclined wellbores.The prior art includes several methods for steering a tool string. Anembodiment of a bent sub system is generally depicted in FIG. 1 a. Inthis embodiment, the drill string comprises a bent sub 2050 above thedrill bit 2051. A hydraulic motor housed within the bore of the drillstring components rotates the drill bit below the bent sub 2050. Asdrilling mud is passed through the drill string the motor turns inresponse to the flow rotating a portion 2052 of the drill string belowthe bent sub. The portion 2053 above the bent sub does not rotate fromthe motor, but slides through the hole as the drill bit advances intothe earth. The bent sub directs the drill strings trajectory in relationto the angle of the bent sub.

An embodiment of a push the bit system is generally depicted in FIG. 1b. In this embodiment, an extendable pad 2150 is located above the drillbit 2051. Typically there is more that one pad oriented around the outersurface of the drill string near the bit that are timed together so asto extend at the same azimuth with relation to the well bore while thedrill string is rotating. Each time a pad extends, it pushes the drillbit off course and may be used to control the drill string's trajectory.

Yet another embodiment for steering bit includes point the bit systemswhere the drill bit is actively positioned from further up the drillstring.

Variations of these systems are disclosed in the following prior artdocuments. U.S. Pat. No. 5,529,133 to Eddison, which is herebyincorporated by reference for all that it contains, discloses asteerable rotary drilling tool that includes a drill bit mounted on thelower end of a housing by a drive shaft having an articulative couplingthat allows the bit's rotation axis to be inclined relative to therotation axis of the housing, an eccentric weight in the housing thatmaintains the bit axis pointed in only one direction in space as the bitis turned by the housing, and a clutch system that allows such directionto be changed downhole. A measuring-while-drilling tool is included toallow the progress of the drilling to be monitored at the surface, andto allow changing the bit axis or toolface by a selected amount.

U.S. Pat. No. 5,078,650 to Foote which is herein incorporated byreference for all that it contains discloses a universal jointarrangement that includes a first adapter having two projecting supportformations; a drive plate having a first pair of matching depressions orpockets is seated with these depressions on the projecting supportformations of the first adapter and the drive plate has a second pair ofpockets for the projecting support formations of a respective secondadapter.

U.S. Pat. No. 7,188,685 to Downton which is herein incorporated byreference for all that it contains discloses a bottom hole assembly thatis rotatably adapted for drilling directional boreholes into an earthenformation. It has an upper stabilizer mounted to a collar, and a rotarysteerable system. The rotary steerable system has an upper sectionconnected to the collar, a steering section, and a drill bit arrangedfor drilling the borehole attached to the steering section. The steeringsection is joined at a swivel with the upper section. The steeringsection is actively tilted about the swivel. A lower stabilizer ismounted upon the steering section such that the swivel is intermediatethe drill bit and the lower stabilizer.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention, a drilling assembly includes adrill bit body disposed intermediate a working face and a shank. Theshank may be attached to a drill string. The working face comprises anindenting member protruding from the working face, the indenting memberbeing adapted to guide the drill bit. A flexible portion is disposedabove the bit body to allow angular deflection of the bit with respectto the drill string.

The flexible portion may comprise upper and lower segments, and may bedisposed intermediate the bit body and the shank or may be disposedintermediate the shank and an adjacent drill string component. The lowersegment of the flexible portion may comprise an extension with agenerally spherical distal end, and a corresponding spherical recess maybe disposed in the upper segment. Bearing balls adapted to transfertorque may be retained in recesses and/or grooves in the sphericalportions of the upper and lower joint segments. In another embodiment,the flexible portion may comprise one or more universal joints. Theportion may comprise a compliant segment. The flexible portion maycomprise a joint with laterally sliding surfaces.

The indenting member may be rotatable with respect to the bit body. Ashaft may be disposed internal to the bit body and intermediate theindenting member and a rotating element such as a fluid-driven turbine,mud motor, or an electric motor. The shaft may be flexible, and maycomprise a compliant portion, one or more universal joints, or aconstant velocity joint.

The indenting member may comprise asymmetrical geometry on the distalend, and may comprise a polycrystalline diamond cutting element. Thepolycrystalline diamond cutting element may comprise pointed geometry.

The assembly may comprise a mechanism adapted to selectively preventmovement of the portion for drilling straight wellbores. The mechanismmay be adapted to selectively limit angular deflection of the flexibleportion, and may self-align the portion to a position of zero angulardeflection.

The assembly may comprise a wiper seal disposed intermediate themoveable sections of the portion. The assembly may also comprise abellows-type seal disposed exterior to the portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a cross-sectional view of an embodiment of the prior art.

FIG. 1 b is a cross-sectional view of another embodiment of the priorart.

FIG. 1 c is a cross-sectional view of an embodiment of a drill stringsuspended in a borehole.

FIG. 2 is a cross-sectional view of an embodiment of a drillingassembly.

FIG. 3 is a cross-sectional view of an embodiment of a drillingassembly.

FIG. 4 is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 5 is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 6 is a perspective view of an embodiment of a universal joint.

FIG. 7 a is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 7 b is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 8 a is a perspective view of an embodiment of an indenting member.

FIG. 8 b is a perspective view of another embodiment of an indentingmember.

FIG. 8 c is a perspective view of another embodiment of an indentingmember.

FIG. 8 d is a perspective view of another embodiment of an indentingmember.

FIG. 9 is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 10 a is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 10 b is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 10 c is a detailed view of another embodiment of a drillingassembly.

FIG. 11 a is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 11 b is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 12 is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 13 is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 14 is a cross-sectional view of another embodiment of a drillingassembly.

FIG. 15 is a diagram of an embodiment of a steering method.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT

FIG. 1 c discloses a drill string 100 suspended in a borehole 103 by aderrick 101. A drilling assembly 102 is connected to the end of thedrill string 100 and comprises a drill bit 104. As the drill bit 104rotates the drill string advances in the formation 105. The drill string100 may comprise one or more flexible portions 106 to allow directionaldrilling.

FIG. 2 discloses an embodiment of a drilling assembly 102. The drillingassembly 102 may comprise a drill bit 104 with a working face 106, anindenting member 107 protruding from the working face 106, and a shank108. A compliant segment 113 may be disposed intermediate the shank 108and a portion of the drill string 109. The compliant segment 113 maycomprise a portion of reduced cross-section 110 to provide elasticangular deflection with respect to an axial centerline of the portion ofthe drill string 109. Cross-sectional area may be reduced by a taper, aseries of circumferential or axial grooves, or one or more helicalgrooves or via a more elastic material. The compliant segment 113 may beconstructed from any material with sufficient strength and suitableelastic modulus, such as high-strength steel or other metal or metalalloy. The drilling assembly 102 may comprise a shaft 111 intermediatethe indenting member 107 and a rotating element 114 such as a fluidpowered turbine, mud motor or an electric motor. The shaft 111 maycomprise a compliant portion 112 to allow deflection in the shaft 111corresponding to the deflection in the compliant segment 113.

The indenting member may be asymmetric such that as it indents into theformation it leads the bit away from straight trajectory. The rotatingelement above may be used to position the apex of the indenting memberat the desired azimuth for the drill string to follow. In such a manner,the driller may control the drill string trajectory. In someembodiments, it may be desirable for the drill string to drill in astraight trajectory, in such cases, the indenting member may be randomlyor otherwise rotated such that it leads the bit in a straight direction.

The ability of the indenting member to steer depends on the ability ofthe asymmetric indenting member to push off of the formation. In softformations, the formation may push back on the indenting member less.Thus, the flexible portion may lower the amount of formation side pushback on the indenting member required to alter the path of the drillbit.

FIG. 3 discloses a drilling assembly 102 according to the presentinvention. The drilling assembly 102 may comprise a drill bit 104 with aworking face 106, an indenting member 107 protruding from the workingface 106, and a shank 108. The shank 108 is connected to a flexibleportion 209. The flexible portion 209 comprises an upper segment 210 anda lower segment 211, the lower segment comprising an extension 212 witha generally spherical portion 213. The upper segment 210 comprises agenerally spherical recess 214 corresponding to the generally sphericalportion 213 of the lower segment 211. The generally spherical portion213 is moveably retained in the generally spherical recess 214. Thegenerally spherical recess 214 comprises a plurality of reliefs 215which hold a plurality of bearing balls 216. The generally sphericalportion 213 of the lower segment 211 comprises a plurality of grooves217, the bearing balls 216 extending into the grooves 217. The bearingballs 216 are free to slide or rotate in the grooves 217 and reliefs215, thus allowing angular deflection of the lower segment 211 withrespect to the upper segment 210, while providing torque transmissionthrough the flexible portion 209 as the drilling assembly 102 rotates.The bearing balls 216 may be retained in a bearing cage. The bearingballs may be constructed from high strength steel and may be casehardened, heat treated, or otherwise processed to provide sufficientstrength. Other suitable materials such as other metals, metal alloys,or ceramic may be used. The reliefs and grooves that retain the bearingballs may also be heat treated, case hardened, or otherwise processed tomitigate abrasive wear.

The upper segment 210 may comprise a mechanism that selectively preventsmovement of the lower segment with respect to the upper segment. In thisembodiment, a plurality of stops 219 are disposed inside the uppersegment 210 and may be brought into contact with the lower segment 211,thus preventing angular deflection of the portion 209 and allowing thedrilling assembly 102 to drill a straight borehole. The plurality ofstops may be actuated by a mechanical, hydraulic, or electronic systemor combinations thereof.

The upper segment 210 of the flexible portion 209 comprises a face 220with convex generally spherical geometry, and the lower segment 211comprises a face 221 with concave generally spherical geometry. Thefaces on the upper and lower segments have a common substantiallyconstant radius of curvature, with the center of curvature in the samelocation as the center of curvature of the generally spherical portion213 and the generally spherical recess 214. The faces 220 and 221 are inslideable contact, thus allowing angular deflection of the lower segment211 with respect to the upper segment 210. The faces 220 and 221 may beheat treated, case hardened, or coated with a wear resistant materialsuch as polycrystalline diamond, a low-friction material such as PTFE,or other wear resistant and/or low friction coating.

The drilling assembly 102 may also comprise a shaft 111 intermediate theindenting member 107 and a rotating element 114 such as a fluid-poweredturbine or electric motor. The shaft 111 may comprise a compliantportion 112 to allow deflection corresponding to the deflection of theflexible portion 209.

Referring now to FIG. 4, the plurality of stops 219 are removed fromcontact with the lower segment 211, thus allowing greater angulardeflection 401 of the lower segment 211 with respect to the uppersegment 210. The indenting member 107 may comprise asymmetrical geometryon the distal end 401. As the drilling assembly 102 rotates, therotating element 114 rotates the shaft 111 with an angular velocityhaving the same magnitude but opposite direction of the angular velocityof the drilling assembly 102. Thus, the indenting member 107 has zeroangular velocity with respect to the formation 105, and the asymmetricalgeometry on the distal end 401 guides the bit 104 through the formation105 in an azimuth direction determined by the orientation of theindenting member 107.

In some embodiments the flexible portion is moved passively inconsequence of the deflections caused by the indenting member.

The plurality of stops 219 may selectively constrain the angulardeflection of the flexible portion 209 to any angle in an intervalincluding zero angle, or non-deviated drilling, to the maximum angleattainable by the flexible portion 209.

FIG. 5 discloses another embodiment of a drilling assembly 102 accordingto the present invention. In this embodiment, the drilling assembly 102comprises a drill bit 104 comprising a working face 106 and a shank 108.A flexible portion 209 is disposed intermediate the working face 106 andthe shank 108. The shank 108 is connected to a drill string 501.

FIG. 6 discloses an embodiment of a universal joint 601. The universaljoint 601 comprises an inner portion 602 and an outer portion 603. Theinner portion 602 is attached to the outer portion 603 by a spider 604comprising bearing carriers 605.

Referring now to FIG. 7 a, a drilling assembly 102 comprises a drill bit104 with a working face 106 and a shank 108. The drill bit 104 comprisesa flexible portion 209 intermediate the working face 106 and the shank108. The flexible portion comprises an upper portion 701 and a lowerportion 702, the lower portion comprising an extension 703. A universaljoint spider 604 comprises generally cylindrical bearing carriers 605and is disposed such that the axial centerline 606 of the bearingcarriers 605 intersects the center of curvature of a generally sphericalinterface 704. The bearing carriers 605 are held in bushings 607 orbearings in the upper portion 701 of the flexible portion 209.

FIG. 7 b discloses the same embodiment as FIG. 7 a, with the drillingassembly 102 rotated 90 degrees. The universal joint spider 604comprises generally cylindrical bearing carriers 608, the axialcenterline 609 of which intersects the center of curvature of thegenerally spherical interface 704. Bearing carriers 608 extend intobushings 610 or bearings disposed in the extension 703 of the lowerportion 702. The bushings 607 and 610 may be made from any suitablematerial including bronze, steel, Babbitt metal, or a polymer.

FIG. 8 a discloses an embodiment of an indenting member 107. In thisembodiment, a polycrystalline diamond compact 801 is brazed or otherwiseaffixed to the distal end of a shank 802. The polycrystalline diamondcompact 801 may be disposed coaxial to the shank 802, and thepolycrystalline diamond compact 801 may comprise pointed geometry. Theshank 802 may be constructed from a steel alloy, and may be casehardened, heat treated, or otherwise processed to improve abrasionresistance. The shank may comprise hard-facing.

FIG. 8 b discloses another embodiment of an indenting member 107. Inthis embodiment, a polycrystalline diamond compact 801 is brazed orotherwise affixed to the distal end of a shank 802. The axial centerlineof the polycrystalline diamond compact 801 and the axial centerline ofthe shank 802 may be offset.

FIG. 8 c discloses another embodiment of an indenting member 107. Ashank 802 comprises a distal end 803 which may be cast, machined,forged, or otherwise formed into a generally polygonal shape. Thegenerally polygonal shape may be asymmetric with respect to the axialcenterline of the shank 802.

FIG. 8 d discloses another embodiment of an indenting member 107. Inthis embodiment, the indenting member 107 comprises a shank 802 and adistal end 803. The distal end 803 may comprise generally conicalgeometry, and may be asymmetric with respect to the axial centerline ofthe shank 802. The distal end 803 may comprise hard-facing or othermaterial or treatment intended to reduce abrasive wear.

FIG. 9 discloses another embodiment of a drilling assembly 102 accordingto the present invention. Drilling assembly 102 comprises a flexibleportion 209 disposed intermediate a drill bit 104 and a portion of drillstring 109. The flexible portion 209 comprises an interface 901intermediate an upper segment 210 and a lower segment 211. The interface901 may be protected from abrasion and wear by a bellows-type cover 902.The cover 902 may be made from electron-beam welded sheet metal oranother material.

The interface 901 may comprise a seal 903 disposed intermediate theupper segment 210 and the lower segment 211. The seal 903 may comprisean o-ring or wiper seal, and may be adapted to retain lubrication on theinterface 901. The interface 901 may be sealed from contact withdrilling fluid, or may be open to the drilling fluid.

A shaft 111 may be disposed intermediate the indenting member 107 and arotating element 114. In this embodiment, the shaft 111 comprises twouniversal joints 904 adapted to allow the shaft 111 to deflect accordingto the deflection of the flexible portion 209.

FIG. 10 a discloses another embodiment of a drilling assembly 102. Inthis embodiment, the drilling assembly comprises a flexible portion 209and includes a sliding collar 1001 comprising ports 1002. Fluid passages1003 are in communication with a plurality of pistons 1004. Pistons 1004are attached to mechanical stops 219.

Referring now to FIG. 10 b, a drilling assembly 102 comprises a slidingcollar 1001. Ports 1002 in the sliding collar 1001 are in communicationwith a plurality of fluid passages 1003. Drilling fluid is diverted intoand creates fluid pressure in passages 1003.

Referring now to FIG. 10 c, which is a detailed view of FIG. 10 b, adrilling assembly 102 comprises a flexible portion 209 and a pluralityof fluid passages 1003. Fluid pressure in the passages 1003 forces aplurality of pistons 1004 and mechanical stops 219 inward to contact alower segment 211 of the flexible portion 209. Flexible portion 209 isthus immobilized to allow drilling straight wellbores.

FIG. 11 a discloses another embodiment of a drilling assembly 102. Inthis embodiment, a lower segment 211 of a flexible portion 209 comprisesa threaded sleeve 1101 engaged with a threaded collar 1102. The threadedsleeve 1101 is free to rotate on an extension 212 of a lower segment 211of the flexible portion 209. An electric motor 1103 rotates the threadedsleeve 1101, and alignment pins 1104 prevent rotation of the threadedcollar. As the electric motor 1103 rotates the threaded sleeve 1101, thenon-rotating threaded collar 1102 moves upward. Maximum angulardeflection of the flexible portion 209 can be controlled by adjustingthe position of the threaded collar, and as the collar moves upward italigns the portion to a position of zero angular deflection.

Referring now to FIG. 11 b, a drilling assembly comprises a threadedcollar 1102 engaged with a rotatable threaded sleeve 1101. The threadedcollar 1102 is in maximum upward position, effectively immobilizing aflexible portion 209 to allow straight drilling.

FIG. 12 discloses another embodiment of a drilling assembly 102. In thisembodiment, a collar 1201 comprises a distal end 1202 with generallyconical geometry 1203. A flexible portion 209 comprises a lower segment211 with an extension 212 which also comprises generally conicalgeometry 1204. The collar may be movable in a direction coaxial with anaxial centerline 1205 of the drilling assembly 102. The position of thecollar 1201 determines the maximum angular deflection of the lowerportion 211 of the flexible portion 209. The position of the collar 1201may be controlled by a mechanical, electronic, hydraulic, or othersystem, or combinations thereof. As the collar 1201 moves toward thelower portion 211 of the flexible portion 209, the generally conicalgeometries 1203 and 1204 are brought into mechanical contact and thelower portion of the joint 211 self-aligns with the collar 1201 and theflexible portion 209 reaches a position of zero angular deflection.

FIG. 13 discloses another embodiment of a drilling assembly 102. A drillbit 104 comprises a plurality of grooves 1301 intermediate a workingface 106 and a shank 108. The grooves 1301 may be circumferential,helical, or otherwise oriented and may be machined, forged, cast, orotherwise formed in the drill bit 104. The grooves 1301 allow forelastic angular deflections in the drill bit 104.

FIG. 14 discloses another embodiment of a drilling assembly 102. Aflexible portion 209 is disposed intermediate a drill bit 104 and aportion of drill string 109. The flexible portion 209 comprises acompliant segment 1401 and an outer sleeve 1402. A collar 1403 ismoveable in a direction coaxial to an axial centerline 1205 of thedrilling assembly 102. Mechanical stops 1404 are disposed internal tothe outer sleeve 1402. The collar 1403 may selectively be brought intomechanical contact with the stops 1401, thus limiting or disallowingangular deflection of the compliant segment 1401 and the drill bit 104.

FIG. 29 is a diagram of a method 2900 for steering a downhole toolstring. The method comprises the steps of providing 2901 a drill bitassembly attached to an end of the tool string disposed within a borehole; providing 2902 a shaft protruding from a working portion of thedrill bit assembly, the working portion comprising at least one cuttingelement; engaging 2903 the formation with a distal end of the shaft, theshaft being part of the drill bit assembly; and angling 2904 the drillbit assembly with the shaft along a desired trajectory. The step ofangling the drill bit assembly with the shaft may comprise angling theshaft or the step may include pushing the drill bit assembly along thedesired trajectory with the shaft. It is believed that if the shaft isloaded with enough pressure that the shaft will penetrate the formation,but if the shaft does not overcome the formation pressure, then theshaft may move the drill bit assembly by pushing off of the formation. Anarrow distal end may aid in concentrating the pressure loaded to theshaft into the formation such that it may overcome the formationpressure and penetrate the formation; on the other hand, a blunt or widedistal end may prevent the shaft from penetrating the formation andallow the shaft to push off of the formation. In some embodiments, theshaft may advance along the desired trajectory before the drill bitassembly. The shaft may be at least partially disposed within a chambergenerally coaxial with the shank portion of the assembly and the chambermay be disposed within a body portion of the assembly. Angling 2904 thedrill bit assembly may be controlled over a downhole network.

In some embodiments, the shaft is rotationally isolated from the workingportion of the drill bit assembly. This may be advantageous because itallows the shaft to remain on the desired trajectory even though theremainder of the drill bit assembly is rotating. In some embodiments ofthe method, the shaft may also rotate with the body portion of the drillbit assembly if there is a plurality of actuators timed to temporallymove the shaft such that the distal end of the shaft stays on thedesired trajectory.

Whereas the present invention has been described in particular relationto the drawings attached hereto, it should be understood that other andfurther modifications apart from those shown or suggested herein, may bemade within the scope and spirit of the present invention.

1. A method for steering a downhole tool string, comprising: providing adrill bit assembly attached to an end of the tool string disposed withina bore hole; providing a shaft protruding from a working portion of thedrill bit assembly; and angularly pushing off the formation with theshaft.
 2. The method of claim 1, wherein pushing off the formationcomprises pushing the drill bit assembly along a desired trajectory bythe shaft.
 3. The method of claim 1, wherein pushing off the formationcomprises angling the shaft.
 4. The method of claim 1, wherein the shaftadvances along the desired trajectory before the drill bit assembly. 5.The method of claim 1, wherein the shaft is disposed within a chambergenerally coaxial with a shank portion of the drill bit assembly.
 6. Themethod of claim 1, wherein the drill bit assembly comprises an actuatorfor angling the distal end of the shaft with respect to a shank portionof the assembly.
 7. The method of claim 6 wherein the actuator isrotationally isolated from a working portion of the drill bit assembly.8. The method of claim 6 wherein the actuator for angling the drill bitassembly is controlled over a downhole network or a downhole tool. 9.The method of claim 1, wherein the shaft is rotationally isolated fromthe bit.
 10. The method of clam 1, wherein a body of the drill bitassembly is adapted to rotate around the shaft.
 11. A method forsteering a downhole tool string, comprising: providing a drill bitassembly attached to an end of the tool string disposed within a borehole; and angularly pushing off the formation in front of the bit with ashaft connected to the drill bit assembly.
 12. The method of claim 11,wherein pushing off the formation comprises pushing the drill bitassembly along a desired trajectory by the shaft.
 13. The method ofclaim 11, wherein pushing off the formation comprises angling the shaft.14. The method of claim 11, wherein the shaft advances along the desiredtrajectory before the drill bit assembly.
 15. The method of claim 11,wherein the shaft is disposed within a chamber generally coaxial with ashank portion of the drill bit assembly.
 16. The method of claim 11,wherein the drill bit assembly comprises an actuator for angling thedistal end of the shaft with respect to a shank portion of the assembly.17. The method of claim 16, wherein the actuator is rotationallyisolated from a working portion of the drill bit assembly.
 18. Themethod of claim 11, wherein the drill bit comprises a flexible portion.19. The method of claim 11, wherein the shaft is rotationally isolatedfrom the bit assembly.
 20. The method of clam 11, wherein a body of thedrill bit assembly is adapted to rotate around the shaft.